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Views: 0 Author: Site Editor Publish Time: 2025-07-30 Origin: Site
The PON module is a core photoelectric conversion device used in passive optical networks. It plays the role of converting optical signals and electrical signals into each other and is a key component for achieving fiber-to-the-home.
The PON module is the core optoelectronic device for building passive optical networks (PON), deployed at both the OLT and ONU ends. It is responsible for converting optical and electrical signals over optical fibers and follows specific PON protocols (such as GPON, XG-PON) to achieve point-to-multipoint communication. The performance of PON modules (rate, wavelength, splitting ratio, etc.) is determined by the standards they follow and is a key technical component for the large-scale and low-cost deployment of fiber broadband access (FTTx). When making a purchase, it is necessary to strictly match the network standards, device compatibility and actual deployment requirements.
The following is a detailed explanation of the PON module:
This is a point-to-multipoint optical fiber access technology architecture.
"Passive" : It refers to the situation in an optical distribution network (ODN) where only splitters without power supply are used for optical power distribution from the central office equipment to the user equipment (such as 1:16, 1:32, 1:64, etc.), and there are no active electronic devices that require power supply. This makes the network structure simple, low-cost, highly reliable and easy to maintain.
Point-to-multipoint: A central office device (OLT) is connected to a splitter via a backbone optical fiber, and the splitter then distributes the signal to multiple user end devices (ONU/ONT).
The main function is to achieve photoelectric conversion.
At the central office (OLT side) : PON module (commonly known as OLT PON module or OLT SFP/SFP+ module)
The downlink electrical signal emitted by the OLT device is converted into an optical signal and sent out through optical fiber.
The uplink optical signal from the user end (ONU) is received and converted into an electrical signal, which is then transmitted to the OLT device for processing.
At the user end (ONU/ONT side) : PON module (usually integrated inside the ONU/ONT device)
The uplink electrical signal emitted by the ONU device is converted into an optical signal and sent to the OLT via optical fiber.
It receives the downlink optical signal from the OLT and converts it into an electrical signal, which is then transmitted to user devices (such as computers, routers, telephones, etc.).
Implementing time-division multiplexing: The PON module adheres to specific PON protocols (such as GPON, XG-PON, EPON, etc.), precisely controlling the transmission and reception timing of data to ensure that the uplink data of multiple ONUs do not conflict on the optical fiber (using TDMA technology).
This is the most important differentiating point. Different standards define different rates, wavelengths, protocols and splitting ratios. Common standards include:
GPON (Gigabit PON) : 2.488 Gbps for downlink and 1.244 Gbps for uplink. It is currently the most mainstream commercial standard.
XG-PON (10G-PON) : Downlink 10 Gbps, uplink 2.5 Gbps (XG-PON) or 10 Gbps (XGS-PON), represents the next-generation evolution of GPON.
EPON (Ethernet PON)/GEPON (Gigabit EPON) : The uplink and downlink are symmetrical at 1.25 Gbps and are mainly popular in some regions (such as Japan and certain areas of China).
NG-PON2 (TWDM-PON) : Utilizing wavelength division multiplexing technology, it offers a higher total bandwidth (such as 40Gbps or more).
50G-PON: The latest standard, offering a downlink rate of up to 50Gbps.
Downlink: Usually, 1490nm (GPON, XG-PON) or 1577nm (XGS-PON, NG-PON2) wavelengths are used for broadcasting to all ONUs.
Uplink: Each ONU uses the same wavelength (typically 1310nm (GPON, EPON) or 1270nm (XG(S)-PON, NG-PON2)), but transmits at different time slices to avoid conflicts.
As defined in the above standard (Gbps level).
Usually within 20 kilometers, with a typical coverage range of 10 to 20 kilometers.
The maximum number of ONUs that an OLT PON port (corresponding to a PON module) can be connected through a splitter. Common ones include 1:32, 1:64, and even 1:128.
On the OLT side, the most common form is the SFP/SFP+ pluggable module, which is convenient for installation and replacement on the service board of the OLT device. There are also XFPS dedicated to higher speeds, etc.
ONU side: It is usually directly integrated on the motherboard of the ONU/ONT device (BOSA component) and is not sold as an independent module to end users.
FTTH (Fiber to the Home) : This is the most important application, providing home users with high-speed broadband, IPTV, VoIP phone and other services.
FTTB (Fiber to the Building)/FTTC (Fiber to the Roadside) : Optical fibers are extended to the vicinity of buildings or communities and then distributed to users through copper wires (such as VDSL) or short-distance optical fibers.
Enterprise dedicated line access: Provide enterprises with high-bandwidth and highly reliable dedicated line services.
Mobile fronthaul/backhaul: In 4G/5G mobile communication networks, it is used to connect base stations (BBU/RRU) and the core network.
Compatible PON standards: They must be fully compatible with the network standards deployed by the operator (such as GPON, XGS-PON).
Compatible OLT/ONU devices: The module needs to be recognized and supported by specific OLT brand models (such as Huawei, ZTE, Nokia, etc.) or ONU devices.
Transmission distance and splitting ratio: Meet the actual network planning requirements.
Working wavelength: Ensure that the uplink and downlink wavelengths comply with the selected standard.
Suppliers and Quality: Select reliable suppliers to ensure the stability, compatibility and service life of the modules.
The SC connector adopts a push-pull structure, which is more convenient to plug and unplug, has a more stable structure, and good mechanical strength. However, its volume is larger than that of the LC connector. The LC connector is smaller in size, only half the size of the SC optical fiber connector, and adopts a plug-in structure with a lock, making it more suitable for high-density cabling. LC connectors are smaller in size, only half the size of SC patch cords, and feature a locking structure, making them more suitable for high-density wiring.
In the following table, I will compare the specific differences between the two:
Parameter | SC connector | LC connector |
Interface size | 2.5 millimeters | The 1.25 mm |
Plugin structure | Push-pull structure | Lockable insertion structure |
Connection accuracy | The accuracy rate is relatively low | The ring is small and the connection accuracy is high |
Grinding method | UPC/APC | It is usually UPC, but there is also APC |
Return loss | UPC: ≥ -50 dB, APC: ≥ -60 dB | UPC: ≥ -50 dB, APC: ≥ -60 dB |
Insertion loss | ≤ 0.3 dB | ≤ 0.25 dB |
Port density | It is large in size and suitable for low-density deployment | It is small in size and suitable for high-density deployment |
Tensile properties | It has high tensile strength and is suitable for complex scenarios | The tensile strength is relatively weak, making it suitable for indoor applications |
Application scenarios | Broadband access network, convergence of the three networks, community FTTH, community cabinet, PON/EPON system | Interconnection among data centers, high-density patch panels, server rooms and backbone switches |
In the field of optical communications, PON (Passive Optical Network) modules are critical components in Fiber-to-the-Home (FTTH) networks. These modules typically use SC connectors (Subscriber Connector) rather than LC connectors (Lucent Connector). This choice is not arbitrary but is based on a combination of technical requirements, application scenarios, and industry standards. Below, we explore the reasons why SC connectors are preferred over LC connectors in PON modules.
SC connectors are larger in size compared to LC connectors, which is significant in the context of PON module applications. PON modules are typically deployed in Optical Distribution Networks (ODNs), such as optical distribution frames (ODFs) or splitters. These environments often require connectors that can withstand physical stress and ensure long-term connection stability. The SC connector’s design offers robust mechanical stability, with its push-pull coupling mechanism ensuring a secure connection and reducing the risk of disconnection due to vibrations or accidental pulls.
In contrast, while LC connectors are smaller and ideal for high-density cabling environments like data centers, their compact size may make them less robust in certain outdoor or harsh environments. Thus, in PON network scenarios, particularly in outdoor or semi-outdoor settings, SC connectors are preferred for their greater physical durability.
SC connectors play a pivotal role in the standardization of PON networks. Standards from the International Telecommunication Union (ITU-T) and other optical communication guidelines, such as those for G.652 fiber, widely recommend SC connectors for PON systems. Many Optical Network Units (ONUs) and Optical Line Terminals (OLTs) are designed with SC interfaces as the standard, ensuring compatibility and interoperability across devices.At present, most manufacturers' GPONOLT devices adopt SC/APC interfaces, and home ONU devices also basically use SC interfaces.
While LC connectors are prevalent in data centers and enterprise networks, the PON ecosystem leans heavily toward SC connectors. This standardized choice reduces adaptation costs for equipment manufacturers and operators while simplifying maintenance and upgrades.
PON networks have stringent requirements for optical power budgets, as signals must be split across multiple end users via optical splitters.
SC connectors are generally ground with APC. In PON systems, especially in long-distance transmission and multi-branch scenarios, the control of optical signal reflection is of great significance. Compared with UPC, APC has lower reflection loss and is more important in cases where the optical power budget is constrained, multi-stage tap connection is required, or more users are mounted on the OLT.
SC connectors typically exhibit lower insertion loss, which helps meet the signal integrity demands of PON networks. Although modern LC connectors have performance levels close to those of SC connectors, during the early days of PON network deployment, SC connectors’ lower insertion loss made them the preferred choice. This historical preference has carried over, becoming an industry norm.
SC connectors are designed for intuitive and convenient installation and maintenance. Their push-pull mechanism allows technicians to quickly connect or disconnect without specialized tools, making them ideal for field operations. In contrast, LC connectors’ latch-based design may require more precise handling, increasing the complexity of field maintenance. In PON network deployments, such as FTTH connections to residential users, technicians often need to perform numerous connections in a short time. The ease of use of SC connectors significantly improves operational efficiency.
The widespread use of SC connectors in PON networks has led to larger production scales and a more mature supply chain, resulting in lower production and procurement costs. While LC connectors offer advantages in high-density applications, their production and adaptation costs have not yet achieved the same economies of scale in the PON market. Operators and equipment manufacturers prefer SC connectors for their cost-effectiveness, optimizing overall network deployment expenses.
The preference for SC connectors over LC connectors in PON modules stems from a combination of factors, including physical durability, industry standards, low insertion loss, ease of operation, and cost-effectiveness. While LC connectors have unique advantages in high-density cabling and data center environments, SC connectors remain the better choice for the specific requirements of PON networks. As optical communication technology continues to evolve, new connector types may emerge, but SC connectors are likely to maintain their dominance in PON networks for the foreseeable future.
